Influence of substrate metallization on diffusion and reaction at the under-bump metallization/solder interface in flip-chip packages


In flip-chip packages, the effect of Ni metallization on the substrate side on interfacial reactions between solders and an Al/Ni(V)/Cu under-bump metallization (UBM) on the chip side was investigated during the reflow process. The Ni substrate metallization greatly accelerated interfacial reactions on the chip side and quickly degraded the thermal stability of the UBM due to a fast consumption of the Ni(V) layer. This phenomenon can be explained in terms of rapid Ni or Sn diffusion in the ternary (Cu,Ni)6Sn5 phase, which was formed in the solder adjacent to the Ni(V) layer and the enhanced dissolution of (Cu,Ni)6Sn5 into the molten solder. Without the Ni metallization on the substrate side, the Al/Ni(V)/Cu UBM remained very stable with both eutectic SnPb and Pb-free solders.

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Zhang, F., Li, M., Chum, C.C. et al. Influence of substrate metallization on diffusion and reaction at the under-bump metallization/solder interface in flip-chip packages. Journal of Materials Research 17, 2757–2760 (2002).

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